THE PRODUCTION of sound is not the fundamental reason for the existence of the mammalian larynx, for there are mammals with larynges and no voices and, on the other hand, mammals with voices and no larynges. The two do not necessarily go together. Since this is true, what then is the basic purpose of the larynx? The larynx is actually a sphincter—a sphincter which physiologically isolates the respiratory tract below it from that above.* This is its primary purpose. There are, throughout the animal kingdom, no exceptions. The ability of the larynx in man to contribute to the production of sound is nothing more than a fortunate side-effect. There are, however, many types of larynges representing many types of sphincters. The human larynx is a three-tiered sphincter—the first being the true vocal cords; the second, the false vocal cords, and the third, the aryepiglottic sphincter. Some larynges, as described in